Hello,
I am running Buster 10.2 on a Lenovo Ideapad 320, and having significant Graphics issues.  I went through the usual suspects (linux-firmware-nonfree, firmware-amd-graphics, etc) and am mostly there.  
In /lib/firmware/amdgpu, there are lots of entries beginning with vega (i.e. vega10 and vega12), but the error messages on bootup state that the missing firmware begins with vega20, which I find in Debian Sid, but not in Buster Stable.
Is there a suggested way to install this Firmware into Buster from Sid, without creating a Franken-Debian?  (And forever living with broken Graphics isn't my first choice.  Also, doing a Complete Install from Sid isn't my Second Choice).
Note:  I didn't check "Backports", when I did the install.  I could add it, if someone thinks vega20 might be there.  Is there a way for me to check?
Thank you in advance!
Kenneth Parker